Thermosetting epoxy resin composition

ABSTRACT

A new thermosetting resin composition is disclosed which comprises a Bisphenol A-type epoxy resin having a number average molecular weight of smaller than 650 but not smaller than 450 and a ratio of the weight average molecular weight thereof to the number average molecular weight thereof of in the range of 1.3-3.0; and a curing agent capable of cross-linking the epoxy resin. The curing agent is preferably a compound represented by the following general formula: ##STR1## wherein X is --CR 1  R 2  --, --CO--, --COO--, --SO 2  --, --SO--, --S--, --O--, --NR 1  --, --SiR 1  R 2  -- or --POR 1  -- where R 1  and R 2  each stands for hydrogen, a lower alkyl or a phenyl; Y and Y&#39; each stands for hydrogen, a lower alkyl or an electron attractive group; R is a lower alkyl; and m and n each is an integer of 1-4, or a mixture thereof with a primary amine, a phenolic compound or an acid anhydride.

This invention relates generally to a thermosetting epoxy resincomposition and, more specifically, to a thermosetting compositioncontaining a specific Bisphenol A-type epoxy resin and affording a curedresin product excellent in hardness, modulus, heat resistance andtoughness.

Because of their excellent resistance to heat and chemicals andexcellent hardness and modulus, epoxy resins have been utilized for awide variety of applications. For example, epoxy resins are known to beused as a matrix material for fiber-reinforced composite plastics. Oneproblem associated with the use of an epoxy resin as a matrix of afiber-reinforced plastic is directed to its low toughness. For example,Japanese Unexamined patent application (Tokkyo Kokai) No. 62-127,317discloses an epoxy resin composition useful for the formation of aprepreg matrix resin, which includes a Bisphenol A-type epoxy resinhaving an epoxy equivalent of 2400-3300 and a number average molecularweight of 3750, and a curing agent. While such an epoxy resincomposition can give improved moldability, the cured resin obtainedtherefrom fails to show satisfactory mechanical strength, particularlytoughness.

The present invention has been made with the above problem ofconventional epoxy resin compositions. In accordance with the presentinvention there is provided a thermosetting composition comprising:

a Bisphenol A-type epoxy resin having a number average molecular weightof smaller than 650 but not smaller than 450 and a ratio of the weightaverage molecular weight thereof to the number average molecular weightthereof of in the range of 1.3-3.0; and

an epoxy resin curing agent capable of cross-linking the epoxy resin.

The thermosetting resin composition according to the present inventioncan afford a cured product having high modulus, hardness and toughnessand excellent resistance to heat and chemicals. Fiber-reinforcedplastics containing a matrix resin obtained from such a thermosettingresin composition exhibit improved mechanical strengths such as impactstrength, fracture strength, resistance to thermal shock and adhesion.Further, the thermosetting resin composition is excellent in tackiness,drape-formability, flowability and stability so that it isadvantageously used for the formation of prepregs. The importantcharacteristic of the epoxy resin composition of the present inventionis that the above properties, especially the tackiness anddrape-formability, are substantially independent of temperature, i.e.these properties are hardly changed with the change in temperature sothat the prepregs exhibit excellent properties in a wide temperaturerange.

The present invention will now be described in detail below.

The term "Bisphenol A-type epoxy resin" used herein is intended to referto an epoxy resin obtained by reaction of Bisphenol A withepichlorohydrin and having as its main ingredient oligomers of thefollowing general formula: ##STR2##

The term "epoxy equivalent", which is also generally called "weight perepoxide equivalent", refers to the weight of the epoxy resin per 1 gramequivalent of the epoxy group contained in the epoxy resin. For example,the epoxy equivalent of the epoxy resin of the above formula in which nis 1 is 312. The Bisphenol A-type epoxy resin to be used in the presentinvention is a mixture of various different molecular weight oligomers.

It is important that the Bisphenol A-type resin to be used in thepresent invention have a number average molecular weight of less than650 but not less than 450 and that the ratio Mw/Mn of the weight averagemolecular weight thereof (Mw) to the number average molecular weightthereof (Mn) is in the range of 1.3-3.0.

In case where the number average molecular weight of the BisphenolA-type epoxy resin to be used in the present invention is lower than450, the tackiness and drape-formability of prepregs containing thethermocurable resin composition becomes poor. Further, the fluidity ofthe epoxy resin composition during its curing stage becomes so high thatit becomes difficult to produce cured products having satisfactorytoughness. Too high a number average molecular weight in excess of 650,on the other hand, is disadvantageous because the tackiness becomes poorat room temperature or below so that lamination of prepregs fails to beeffected satisfactory. The number average molecular weight of the epoxyresin is preferably smaller than 650 but not smaller than 500.

When the ratio Mw/Mn is below 1.3, the amount of low molecular weightcomponents becomes so large that there are caused such defects as seenin the case of using a Bisphenol A-type epoxy resin having a numberaverage molecular weight of less than 450. On the other hand, a ratioMw/Mn of above 3.0 also causes such defects as seen in the case of usinga Bisphenol A-type epoxy resin with a number average molecular weight of650 or more because the content of high molecular weight componentsbecomes high.

The Bisphenol A-type epoxy resin to be used in the present invention canbe obtained by blending two or more commercially available BisphenolA-type resins. Examples of suitable resins include Epicoat 815, 827,828, 834, 1001, 1002, 1004, 1007, 1009, 1010 (Trademarks of Yuka-ShellKabushiki Kaisha) whose epoxy equivalents and molecular weights areshown below:

    ______________________________________                                                                Number Average                                        Epicoat    Epoxy Equivalent                                                                           Molecular Weight                                      ______________________________________                                         815       181-191       330                                                   827       180-190                                                             828       184-194       380                                                   834       230-270       470                                                  1001       450-500       900                                                  1002       600-700      1060                                                  1004       800-900      1600                                                  1007       1750-2200    2900                                                  1009       2400-3300    3750                                                  1010       3000-5000    5500                                                  ______________________________________                                    

The Bisphenol A-type epoxy resin may be obtained, for example, byblending a first resin having an epoxy equivalent of 180-195 with asecond resin having an epoxy equivalent of greater than 195, the amountand the molecular weight of the second resin being such as to provide aratio Mw/Mn and a number average molecular weight of the blend of1.3-3.0 and 450-650, respectively. The first resin may be Epicoat 815,827, 828 or a mixture thereof while the second resin may be Epicoat 834,1001, 1002, 1004, 1007, 1009, 1010 or a mixture thereof.

When an improvement in heat resistance is desired at the sacrifice oftoughness, an epoxy resin which is not a Bisphenol A-type epoxy resincan be incorporated into the thermosetting epoxy resin composition.However, the amount of such an additional epoxy resin should not exceed50 % by weight based on the total weight of the Bisphenol A-type epoxyresin and the additional epoxy resin, since otherwise there is caused aconsiderable reduction in toughness.

Examples of such additional epoxy resins include glycidyl ether-typeepoxy resins such as Bisphenol F-type, Bisphenol S-type, novolac typeand brominated Bisphenol A-type epoxy resins; alicyclic epoxy resins;glycidyl ester-type epoxy resins; glycidylamine-type epoxy resins; andheterocyclic epoxy resins.

Any curing agent may be used in the present invention. The curing agentis generally used in a schiometric amount with respect to the epoxyresin. Examples of the curing agents include:

(A) Amine curing agent:

(A-1) aliphatic primary amines such as diethylenetriamine,triethylenetetramine, tetraethylenepentamine, dipropylenetriamine,trimethylhexamethylenediamine, a polyether diamine,diethylaminopropylamine, menthendiamine, methaxylylenediamine and3,9-bis(3-aminopropyl)-2,4,8,10-tetraspiro[5,5]undecane; (A-2) aromaticprimary amines such as methaphenylenediamine, diaminodiphenylmethane,diaminodiphenylsulfone, and aromatic diamine eutectic mixtures;

(A-3) modified amines such as amine adducts and cyanoethylatedpolyamines;

(A-4) secondary and tertiary amines such as tetramethylguanidiene,pyperidine, pyridine, picoline, benzyldimethylamine,2-(dimethylaminomethyl)phenol; and

(A-5) polyamides such as condensation products of a dimer acid with apolyamine;

(B) acid anhydrides:

(B-1) aromatic acid anhydrides such as phthalic anhydride, trimelliticanhydride, ethylene glycol bis(anhydrotrimellitate), glyceroltris(anhydrotrimellitate), pyromellitic anhydride and3,3',4,4'-benzophenone tetracarboxylic anhydride;

(B-2) alicyclic acid anydrides such as maleic anhydride, succinicanhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalicanhydride, methylnadic anhydride, alkenylsuccinic anhydride,hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, andmethylcyclohexene tetracarboxylic anhydride;

(B-3) aliphatic acid anhydrides, halogenated acid anhydrides,polycarboxylic anhydride and chloreside anhydride;

(C) polyamide resins such as N,N'-bis(6-aminohexyl)adipamide; (D)imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole,2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole,1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole,1-cyanoethyl-2-undecylimidazolium trimellitate,2,4-diamino-6-[2-methylimidazolyl-(1)]-ethyl-S-triazine,1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-phenylimidazoliumisocyanulate, and 2-phenyl-4-methyl-5-hydroxymethylimidazole;

(E) boron trifluoride-amine complexes;

(F) dicyanodiamide and its derivatives such as o-tolyl biguanide andα-2,5-dimethylbiguanide;

(G) organic acid hydrazides such as succinic acid hydrazide and adipicacid hydrazide;

(H) diaminomaleonitrile and its derivatives;

(I) melamine and its derivatives such as diallylmelamine;

(J) amine imides;

(K) polyamines;

(L) oligomers such as novolac phenol resins, novolac cresol resins andpoly-p-vinylphenols.

When the thermosetting epoxy resin composition of the present inventionis to be used for the formation of molded articles such as mechanicalparts, the use of diaminodiphenylmethane, diaminodiphenylsulfone anddicyanodiamide as the curing agent is preferred for reasons ofobtainability of suitable toughness, heat resistance and machinability.

When the thermosetting epoxy resin composition is intended to be usedfor a carbon fiber-reinforced prepreg matrix, the use of dicyanodiamide,diaminodiphenylmethane and diaminodiphenylsulfone is also preferred forreasons of obtainability of suitable tackiness, drape-formability,flowability, workability and stability.

It is especially preferable to use as the curing agent at least onecompound represented by the following general formula (I): ##STR3##wherein X is --CR₁ R₂ --, --CO--, --COO--, --SO₂ --, --SO--, --S--,--O--, --NR₁ --, --SiR₁ R₂ -- or --POR₁ -- where R₁ and R₂ each standsfor hydrogen, a lower alkyl or a phenyl; Y and Y' each stands forhydrogen, a lower alkyl or an electron attractive group; R is a loweralkyl; and m and n each is an integer of 1-4.

Preferably, in the above formula (I), R is an alkyl having 1-3 carbonatoms, X is --CH₂ --, --SO₂ --, --CO--, --O--, --C(CH₃)₂ -- or --CHC₆H₅, Y and Y' each is hydrogen, a lower alkyl, a halogene, a nitro groupor trifluoromethyl, R₁ and R₂ each is an alkyl having 1-3 carbon atoms,and m and n each is 1 or 2. Illustrative of suitable compounds of theformula (I) are as follows: ##STR4##

The use of the compound of the formula (I) can give a cured epoxy resinproduct having an improved toughness. It is desirable to use thecompound of the formula (I) in conjunction with another curing agentselected from primary amines such as aliphatic amines, aromatic amines,polyamidoamines and dicyanopolyamides; phenolic compounds such asbisphenols, phenolic resins, vinylphenol polymers; acid anhydrides suchas maleic anhydride, succinic anhydride, methyltetrahydrophthalicanhydride, methylnadic anhydride and methylhexahydrophthalic anhydride;and mixtures thereof. Of these, the use of diaminodiphenylsulfone,diaminodiphenylmethane, dicyanodiamide or methylhexahydrophthalicanhydride is particularly preferred. By using the compound (I) with theabove curing agent, the resulting cured product exhibits such excellenttoughness, heat resistance, rigidity, mechanical strengths and otherproperties that are not expected from the use of them separately.

Such a synergetic effect is considered to result from a unique structureof the cured product. That is, when an epoxy resin is reacted with themixed-type curing agent at an elevated temperature, there are formed, atan early stage of the curing, high molecular weight, linear polymers asa result of the reaction of the epoxy resin and the second curing agenthaving two secondary amino groups, which is considered to contribute toimprovement in toughness of the resulting cured product. The hydroxylgroups of the linear polymers thus formed further react, at a laterstage of the curing, with the glycidyl groups of the epoxy resin. At thesame time, the first curing agent reacts with the epoxy resin. These twocross-linking reactions are considered to contribute to improvement inregidity and mechanical strengths of the cured product. Thus, the curinginvolves at least the above three types of cross-linking reactions whichproceed homogeneously and continuously to give the cured product havingcomplicated cross-linkages and uniform morphology.

The proportion of these two types of curing agents may be arbitrary.Preferably, these two curing agents are used in amounts so that thecompound of the formula (I) accounts for 15 to 95 %, preferably 25 to 75%, of a total of the amounts of active hydrogen of the two curingagents. The amount of the mixed curing agent is preferably such as toprovide a ratio of equivalents of the active hydrogen of the mixedcuring agent per equivalent of the epoxy group of the epoxy resin of inthe range of 0.6-1.4, more preferably 0.8-1.2.

For preparing the thermosetting composition according to the presentinvention, the curing agent may be mixed as is or in the form of asolution in a solvent with the Bisphenol A-type epoxy resin. The solventmay be, for example, a ketone such as acetone, methyl ethyl ketone ormethyl isobutyl ketone; a cellosolve such as methyl cellosolve or ethylcellosolve; an amide such as dimethyl formamide. The mixing may beperformed at room temperature or, to facilitate homogeneous mixing, atelevated temperatures.

If desired, one or more additives may be incorporated into the resinmixtures. Illustrative of such additives are a reactive diluent such asolefin oxide, glycidyl methacrylate, styrene oxide or phenylglycidylether, a curing accelerator such as phenol, a tertiary amine, imidazole,a boron trifluoride complex salt, pyrazole or aminotriazole, and afiller such as silica powder, alumina powder, mica or calcium carbonate.Amounts of these additives may generally range up to 15 % by weight forthe reactive diluent, up to 5 % by weight for the curing accelerator,and up to 70 % by weight for the filler based on the total weight of theepoxy resin and the curing agent.

The curing is generally performed at temperatures of 100°-140° C. for1-3 hours. This may be followed, if desired, by a post curing treatmentwhich may be performed at 150°-220° C. for 1-3 hours.

The thermosetting composition according to the present invention canprovide a matrix resin, for example, for civil engineering andconstruction materials, coatings, lining materials, adhesives, moldedmaterials, for electrical appliances (for example, mechanical parts,jigs and tools), fiber reinforced plastic composite materials and thelike. The cured, epoxy resin articles obtained using the thermocurablecomposition of the present invention has excellent heat resistance,modulus, hardness, chemical resistance, toughness, flexibility,rigidity, strength, anti-cracking property, impact strength and rupturestrength. It is especially suited as an FRP matrix resin for theproduction of composite articles with high mechanical strength.

The following examples will further illustrate the present invention.

PREPARATION EXAMPLE 1

In 276 g (1 mole) of diaminodiphenylsulfone (DDS) in 1000 ml of a mixedsolvent of water/ethanol (50/50) was charged 284 g (2 moles) of methyliodide (CH₃ I), and the mixture was reacted at 60° C. for 2 hours. Theresulting crude product was purified by recrystallization with awater/ethanol (50/50) mixed solvent in duplicate.

The resulting product is identified by infrared absorption spectrum (IR)and gel permeation chromatography (GPC) and confirmed to be a pureproduct of an epoxy resin curing agent (B), the objective productaccording to the present invention, represented by the followingformula: ##STR5##

PREPARATION EXAMPLE 2

In 198 g (1 mole) of diaminodiphenylmethane (DDM) in 1000 ml of a mixedsolvent of water/ethanol (50/50) was charged 284 g (2 moles) of methyliodide (CH₃ I), and the mixture was reacted at 60° C. for 2 hours. Theresulting crude product was purified by recrystallization with awater/ethanol (50/50) mixed solvent in duplicate.

The resulting product is identified by IR and GPC and confirmed as apure product of an epoxy resin curing agent (B), the objective productaccording to the present invention, represented by the followingformula: ##STR6##

PREPARATION EXAMPLES 3-5

In place of diaminodiphenyl sulfone (DDS) used in Preparation Example 1,the process of Preparation Example 1 was followed in the same mannerwith the exception to use compounds of the following general formula:##STR7## (in which X is --CO--, --S-- or --C(CH₃)₂ --), yielding thefollowing compounds: ##STR8##

PREPARATION EXAMPLE 6

In place of diaminodiphenylsulfone (DDS) used in Preparation Example 1,the process of Preparation Example 1 was followed in the same mannerwith the exception to use a compound of the following general formula:##STR9## yielding a compound of the formula: ##STR10##

PREPARATION EXAMPLE 7

In a solution of 198 g (1 mole) of N,N-diaminodiphenylmethane (DDM) in1,000 ml of a water/ethanol (50/50) mixed solvent was charged 312 g (2moles) of ethyl iodide (C₂ H₅ I), and the mixture was reacted at 60° C.for 3 hours. The resulting crude product was recrystallized twice from awater/ethanol (50/50) mixed solvent.

The resulting reaction product was identified by means of IR and GPC tohave the following formula: ##STR11##

PREPARATION EXAMPLE 8

In place of diaminodiphenylsulfone (DDS) used in Preparation Example 1,the process of Preparation Example 1 was followed in the same mannerwith the exception to use a compound of the following general formula:##STR12## yielding a compound of the formula: ##STR13##

EXAMPLE 1

Epoxy resins were blended in amounts shown in Table 1 below and theresulting blend was heated to 150° C. to obtain a homogeneous mixture.After cooling to 80° C., dicyanodiamide was mixed to the mixture in astoichiometric amount, thereby to obtain a thermosetting composition.The composition was poured into a mold composed of two glass platesspaced apart from each other by a Teflon spacer, heated at 100° C. for 2hours, and then cured at 200° C. for 2 hours in an oven. The curedproduct was sliced into test pieces with a size of 30 cm×30 cm×3 mm andthe test pieces were subjected tested for Izod strength (IZOD) and glasstransition temperature (Tg) to obtain the results summarized in Table 1.A prepreg was also prepared by impregnating carbon fibers (tensilestrength: 350 kg/mm², modulus: 32 t/mm²), arranged in parallel with eachother, with the above epoxy resin composition. Workability for thefabrication of the prepreg was good. The prepreg showed the tackiness(TAC) at 23° C. as shown in Table 1. Temperature dependency (TDP) of thetackiness was tested at several temperatures in the range of 15°-30° C.to reveal that no substantial change in tackiness was caused with thechange in temperature. Similar prepregs (12 sheets) were laminated andthe laminate was cured under the same conditions as above to obtaincarbon fiber-reinforced composite material whose compression afterimpact (CAI) was as shown in Table 1.

The tackiness (TAC) and temperature dependency (TDP) were evaluatedaccording to the following ratings:

TAC (at 23° C.)

A: good

B: relatively bad

C: poor

TDP (15°-30° C.)

A: no substantial change

B: significant change

EXAMPLES 2-5

Example 1 was repeated in the same manner as described except thecompositions of the epoxy resin blends were changed as shown in Table 1.The results were as summarized in Table 1. The workability for thefabrication of the prepreg was good in the case of Examples 2-4. InExample 5, other epoxy resin (Epicoat 152 manufactured by Yuka ShellInc., epoxy equivalent: 172-179, number average molecular weight: 370)than the Bisphenol A-type was additionally used.

COMPARATIVE EXAMPLES 1-5

Example 1 was repeated in the same manner as described except thecompositions of the epoxy resin blends were changed as shown in Table 1.The results were as summarized in Table 1. The toughness is poor inComparative Examples 1, 2 and 4. In the case of Comparative Examples 3and 5, good prepreg was not obtained.

                                      TABLE 1                                     __________________________________________________________________________    Amount (wt %)                                                                 Epicoat                        Izod   Tg CAI                                  Example                                                                            828                                                                              1001                                                                             1004                                                                             1007                                                                             1010                                                                             152                                                                              Mn Mw/Mn                                                                              (kg · cm/cm.sup.2)                                                          (°C.)                                                                     (kg/mm.sup.2)                                                                       TAC                                                                              TDP                         __________________________________________________________________________    1    60    10 30    152                                                                              573                                                                              2.2  6.0    121                                                                              23    A  A                           2    60       40       582                                                                              2.4  6.8    120                                                                              26    A  A                           3    50 10 20 20       617                                                                              1.9  7.5    120                                                                              27    A  A                           4    50    25 25       642                                                                              2.1  8.1    121                                                                              29    B  A                           5    30    25 25    20 636                                                                              2.1  5.3    125                                                                              23    A  A                           Comp. 1                                                                            100               380                                                                              1.0  2.2    135                                                                              12    C  B                           Comp. 2                                                                            50 50             534                                                                              1.2  2.4    120                                                                              14    B  B                           Comp. 3                                                                            70          30    527                                                                              3.6  6.9    120                                                                              27    B  B                           Comp. 4                                                                            20    20       60 440                                                                              1.4  1.9    126                                                                              12    B  B                           Comp. 5                                                                            40    20 40       760                                                                              2.2  8.1    119                                                                              29    C  B                           __________________________________________________________________________

EXAMPLES 6, 7, 9 AND 10

Examples 1, 2, 4 and 5 were repeated in the same manner as describedexcept that the compound obtained in Preparation Example 2 was used asthe curing agent in place of dicyanodiamide. The results are summarizedin Table 2.

EXAMPLE 8

Example 2 was repeated in the same manner as described except that thecompound obtained in Preparation Example 1 was used as the curing agentin place of dicyanodiamide. The results are summarized in Table 2.

COMPARATIVE EXAMPLES 6 AND 9-11

Comparative Examples 1 and 3-5 were repeated in the same manner asdescribed except that, as the curing agent, the compound obtained inPreparation Example 2 was used in place of dicyanodiamide. The resultsare summarized in Table 2.

COMPARATIVE EXAMPLE 7

Comparative Example 1 was repeated in the same manner as describedexcept that, as the curing agent, the compound obtained in PreparationExample 1 was used in place of dicyanodiamide. The results aresummarized in Table 2.

COMPARATIVE EXAMPLE 8

Comparative Example 6 was repeated in the same manner as describedexcept that a mixed Bisphenol A-type resin having the composition shownin Table 2 was used. The results are summarized in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Amount (wt %)                     Izod    CAI                                 Epicoat                   Mw/                                                                              Curing                                                                             (kg · cm/                                                                 Tg (kg/                                Example                                                                            828                                                                              1001                                                                             1004                                                                             1007                                                                             1010                                                                             152                                                                              Mn Mn agent*                                                                             cm.sup.2)                                                                          (°C.)                                                                     mm.sup.2)                                                                         TAC                                                                              TDP                          __________________________________________________________________________    6    60    10 30       573                                                                              2.2                                                                              MeDDM                                                                              13.5 121                                                                              45  A  A                            7    60       40       582                                                                              2.4                                                                              MeDDM                                                                              15.2 119                                                                              46  A  A                            8    60       40       582                                                                              2.4                                                                              MeDDS                                                                               9.9 196                                                                              40  A  A                            9    50    25 25       642                                                                              2.1                                                                              MeDDM                                                                              15.6 118                                                                              49  B  A                            10   30    25 25    20 636                                                                              2.1                                                                              MeDDM                                                                              13.5 126                                                                              45  A  A                            Comp. 6                                                                            100               380                                                                              1.0                                                                              MeDDM                                                                              11.2 135                                                                              42  C  B                            Comp. 7                                                                            100               380                                                                              1.0                                                                              MeDDS                                                                               7.0 205                                                                              35  C  B                            Comp. 8                                                                            80 20             430                                                                              1.1                                                                              MeDDM                                                                              11.6 120                                                                              42  B  B                            Comp. 9                                                                            70          30    527                                                                              3.6                                                                              MeDDM                                                                              15.3 118                                                                              45  B  B                            Comp. 10                                                                           40    20 40       760                                                                              2.2                                                                              MeDDM                                                                              15.7 117                                                                              49  C  B                            Comp. 11                                                                           20    20       60 440                                                                              1.4                                                                              MeDDM                                                                               5.8 129                                                                              29  B  B                            __________________________________________________________________________     *Number of Preparation Example                                           

EXAMPLES 11-15

Example 2 was repeated in the same manner as described except thatvarious mixed curing agents as shown in Table 3 were each used in placeof dicyanodiamide. The results were as summarized in Table 3.

EXAMPLES 16-17

Examples 4 and 5 were repeated in the same manner as described exceptthat a mixed curing agent as shown in Table 3 was used in place ofdicyanodiamide. The results are shown in Table 3.

COMPARATIVE EXAMPLES 13-15

Comparative Examples 8, 9 and 11 were repeated in the same manner asdescribed except that a mixed curing agent as shown in Table 3 was usedin place of the compound of Preparation Example 2. The results are shownin Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Amount (wt %)                Curing agent                                                                            Izod    CAI                            Epicoat                   Mw/                                                                              (A)                                                                              (B)    (kg · cm/                                                                 Tg (kg/                           Example                                                                            828                                                                              1001                                                                             1004                                                                             1007                                                                             1010                                                                             152                                                                              Mn Mn *1 *2  A:B                                                                              cm.sup.2)                                                                          (°C.)                                                                     mm.sup.2)                                                                         TAC                                                                              TDP                     __________________________________________________________________________    11   60       40       582                                                                              2.4                                                                              (2)                                                                              DDM 75:25                                                                            16.0 127                                                                              44  A  A                       12   60       40       582                                                                              2.4                                                                              (2)                                                                              DDM 50:50                                                                            17.0 129                                                                              57  A  A                       13   60       40       582                                                                              2.4                                                                              (2)                                                                              DDM 30:70                                                                            16.1 133                                                                              53  A  A                       14   60       40       582                                                                              2.4                                                                              (1)                                                                              DICY                                                                              30:70                                                                            12.0 202                                                                              45  A  A                       15   60       40       582                                                                              2.4                                                                              (2)                                                                              DICY                                                                              30:70                                                                            17.2 130                                                                              58  A  A                       16   50    25 25       642                                                                              2.1                                                                              (2)                                                                              DICY                                                                              30:70                                                                            17.5 127                                                                              60  B  A                       17   30    25 25    20 636                                                                              2.1                                                                              (2)                                                                              DICY                                                                              30:70                                                                            13.2 130                                                                              47  A  A                       Comp. 13                                                                           80 20             430                                                                              1.1                                                                              (2)                                                                              DICY                                                                              30:70                                                                            15.2 129                                                                              51  B  B                       Comp. 14                                                                           70          30    527                                                                              3.6                                                                              (2)                                                                              DICY                                                                              30:70                                                                            16.9 128                                                                              52  B  B                       Comp. 15                                                                           20    20       60 440                                                                              1.4                                                                              (2)                                                                              DICY                                                                              30:70                                                                             6.0 130                                                                              30  B  B                       __________________________________________________________________________     *1: The number of Preparation Example                                         *2: DDS: diaminodiphenylsulfone, DDM: N,Ndiaminodiphenylmethane, DICY:        dicyanodiamide                                                           

Details of the results of the temperature dependency tests for theprepregs of Examples 3, 7 and 15 and Comparative Examples 2, 5, 8, 10and 13 are summarized in Table 4. The tackiness value was measured inthe following manner.

Paper was coated with molten epoxy resin composition to be tested with athickness of about 30 um. The coated paper was cut into strips having awidth of 10 mm. The resulting strip was attached to each of upper andlower holders of a tackiness measuring device (PICMATAC manufactured byToyo Seiki Co., Ltd.). The two paper strips were then contacted bymoving the holders with a predetermined pressure for a predeterminedperiod of time at various temperatures (15° C., 23° C. and 30° C.).Thereafter, the holders were moved backward at a speed of 20 mm/minute.The stress required for separating the contacted strips from each otherwas measured. This stress (g) represents the tackiness value of thesample at that temperature.

                  TABLE 4                                                         ______________________________________                                                         Tackiness value (g)                                          Example No.                                                                             Mn      Mw/Mn    15° C.                                                                        23° C.                                                                       30° C.                         ______________________________________                                        3         617     1.9      215    270   235                                   Comp. 2   534     1.2      380    320   115                                   Comp. 5   760     2.2       70    170   385                                   7         582     2.4      220    230   250                                   Comp. 8   430     1.1      280    150   110                                   Comp. 10  760     2.2       30    160   250                                   15        582     2.4      250    270   270                                   Comp. 13  430     1.1      290    160   115                                   ______________________________________                                    

As will be appreciated from the results shown in Table 4, with the epoxyresin composition according to the present invention, the tackinessvalues are maintained in the optimum range of 200-300 g irrespective ofthe temperature change. On the other hand, with the epoxy resincompositions having a number average molecular weight Mn greater than650 (Comparative Examples 5 and 10), the tackiness considerablyincreases with the increase of the temperature. When the Mn is lowerthan 450 (Comparative Examples. 8 and 13) or when the Mw/Mn is below 1.3(Comparative Example 2), the tackiness considerably decreases with theincrease of the temperature. Such temperature dependency causes muchdifficulty in the preparation of prepregs.

What is claimed is:
 1. A thermosetting resin composition comprising:aBisphenol A derived epoxy resin having a number average molecular weightsmaller than 650 but not smaller than 450 and a ratio of the weightaverage molecular weight thereof to the number average molecular weightthereof in the range of 1.3-3.0; and at least one epoxy resin curingagent capable of cross-linking the epoxy resin and having the followingformula: ##STR14## wherein X is --CR₁ R₂ --, --CO--, --COO--, --SO₂ --,--SO--, --S--, --O--, --NR₁ --, --SiR₁ R₂ -- or --POR₁ -- wherein R₁ andR₂ each stands for hydrogen, a lower alkyl or a phenyl; Y and Y' eachstands for hydrogen, a lower alkyl or an electron attractive group; R isa lower alkyl; and m and n each is an integer of 1-4.
 2. A compositionas set forth in claim 1, wherein the Bisphenol A-type epoxy resin has anumber average molecular weight of smaller than 650 but not smaller than500 and the ratio of the weight average molecular weight thereof to thenumber average molecular weight thereof is in the range of 1.5-2.7.
 3. Acomposition as set forth in claim 1, further comprising an additionalepoxy resin other than a Bisphenol A-type epoxy resin in an amount 50 %by weight or less based on the total weight of said Bisphenol A-typeepoxy resin and said additional epoxy resin.
 4. A composition as setforth in claim 1, wherein said Bisphenol A-type epoxy resin is a blendof a first, Bisphenol A-type epoxy resin having an epoxy equivalent inthe range of 180-195 with a second, Bisphenol A-type epoxy resin havingan epoxy equivalent of greater than 195, the amount and the molecularweight of said second epoxy resin being such that the blended BisphenolA-type epoxy resin has a number average molecular weight of smaller than650 but not smaller than 450 and the ratio of the weight averagemolecular weight thereof to the number average molecular weight thereofis in the range of 1.3-3.0.
 5. A composition as set forth in claim 1,wherein R is an alkyl having 1-3 carbon atoms, X is --CH₂ --, --SO₂ --,--CO--, --O--, --C(CH₃)₂ -- or --CHC₆ H₅ --, Y and Y' each is hydrogen,a lower alkyl, a halogene, a nitro group or trifluoromethyl, R₁ and R₂each is an alkyl having 1-3 carbon atoms, and m and n each is 1 or
 2. 6.A thermosetting resin composition comprising:a Bisphenol A derived epoxyresin having a number average molecular weight smaller than 650 but notsmaller than 450 and a ratio of the weight average molecular weightthereof to the number average molecular weight thereof in the range of1.3-3.0; and an epoxy resin curing agent capable of cross-linking theepoxy resin and comprising a first element which is at least one memberselected from primary amines, phenolic compounds and acid anhydrides,and a second element which is at least one of the compounds representedby the following general formula: ##STR15## wherein X is --CR₁ R₂ --,--CO--, --COO--, --SO₂ --, --SO--, --S--, --O--, NR₁ --, --SiR₁ R₂ -- or--POR₁ -- wherein R₁ and R₂ each stands for hydrogen, a lower alkyl or aphenyl; Y and Y' each stands for hydrogen, a lower alkyl or an electronattractive group; R is a lower alkyl; and m and n each is an integer of1-4.
 7. A composition as set forth in claim 6, wherein said first andsecond elements are used in amounts so that said first and secondelements account for 85 to 5% and 15 to 95%, respectively, of a total ofthe amounts of active hydrogen of said first and second elements.
 8. Acomposition as set forth in claim 6, wherein said first element is atleast one member selected from aliphatic primary amines, aromaticprimary amines, polyamido primary amines, dicyanopolyamides, bisphenols,phenolic resins, vinylphenol polymers, maleic anhydride succinicanhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride andmethylhexahydrophthalic anhydride.
 9. A composition as set forth inclaim 8, wherein wherein said first element is diaminodiphenyl sulfone,diaminodiphenyl methane, dicyanodiamide or methylhexahydrophthalicanhydride.
 10. A composition as set forth in claim 6, wherein R is analkyl having 1-3 carbon atoms, X is --CH₂ --, --SO₂ --, --CO--, --O--,--C(CH₃)₂ -- or --CHC₆ H₅ --, Y and Y' each is hydrogen, a lower alkyl,a halogene, a nitro group or trifluoromethyl, R₁ and R₂ each is an alkylhaving 1-3 carbon atoms, and m and n each is 1 or
 2. 11. A compositionas set forth in claim 6, wherein the curing agent is used in an amountproviding a ratio of equivalents of the active hydrogen of the curingagent per equivalent of the epoxy group of the epoxy resin of in therange of 0.6-1.4.